Saturn's Rings Older Than First Thought?

By Alicia Chang, AP Science Writer |
December 13, 2007 09:58am ET

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Saturn's magnificent rings star in this donut-like view taken by the Cassini spacecraft. The planet itself has been removed from view, blotted out to highlight the intricate set of rings as Cassini passed over head at an elevation of about 60 degrees - the probe's highest yet vantage point of Saturn. This image is actually a compilation of 27 separate views - nine separate sets of red, green and blue components - taken over about 45 minutes and then assembled into a mosaic by scientists on Earth. It is one of several released March 1, 2007 by NASA, though the image group was taken in late January, 2007. Cassini used its wide-angle camera to photograph Saturn's rings from a distance of about one million miles (1.6 million kilometers). The moons Epimetheus (in the one o'clock position), Pandora (at five o'clock), and Janus (10 o'clock) are visible in this view.

Astronomers had thought Saturn's rings were cosmically
young, likely born some 100 million years ago from leftovers of a meteoric
collision with a moon, based on data by NASA's Voyager spacecraft in the 1970s.

However, new data from the orbiting international Cassini
spacecraft suggest the rings existed as far back as 4.5 billion years ago,
roughly the same time the sun and planets formed. The probe also found evidence
that ring particles are constantly shattering and regrouping to form new rings.

"Recycling allows the rings to be as old as the solar
system although continually changing,'' said Larry Esposito, a Cassini
scientist from the University of Colorado.

The findings were presented at an American Geophysical Union
meeting in San Francisco and will be published in the astronomical journal
Icarus.

Saturn's
trademark arcs have awed astronomers since Galileo's time. Scientists are
interested in the rings because they are a model of the disk of gas and dust
that initially enveloped the sun and studying them could yield clues about planet
formation.

Saturn's
ring system consists of seven major rings and thousands of ringlets, mostly
made of orbiting ice mixed with dust and rock fragments.

The notion that Saturn's rings may be a permanent feature
was based on observations by the ultraviolet spectrograph instrument on
Cassini, which viewed the light reflected from the rings and watched stars
passing behind them.

The Cassini mission, funded by NASA and the European and
Italian space agencies, was launched in 1997 and reached Saturn in 2004. The
mission is managed by NASA's Jet Propulsion Laboratory in Pasadena.